Windows are the eyes peering into the soul of your home. They protect us from inclement weather, allow us to connect with the outdoors and, most importantly, let the light in. However, while windows permit views and light, they also permit unwanted heat gain and unwanted heat loss. In fact approximately one-third of a typical home’s energy dollars are thrown out of the windows.

Double-Paned and Triple-Paned Windows

Double-paned, triple-paned, or even quadruple-paned windows are exactly what they sound like – two, three, or even four single panes of glass sandwiched together to create a super-efficient window assembly. Think of it like layers of clothing during the winter. They prevent infiltration – or unintentional air leakage. The spaces between panes in multi-pane windows can also be pumped with inert gases, such as argon. Inert gases are excellent insulators and further enhance the effectiveness of the window. A key figure to look for is the U-value, or U-factor. The rate of heat loss through a window is indicated in terms of this number. Therefore the lower the indicated number, the better. Double-paned windows typically have U-factors of 0.30 or lower. Triple and quadruple-paned windows can get as low as 0.15.

Low-E. Low Bills.

The amount of heat from direct sunlight gained through a window is measured as Solar Heat Gain Coefficient (SHGC). A lower number indicates that less heat is allowed through the window. While window tints are a justifiably effective way of eliminating unwanted heat gain, they often reduce visibility. What is needed is a selective filter that will let in natural light, without reducing visibility, while selectively blocking out heat. This can be accomplished through the use of low-e, or low emissivity, films which selectively block radiant infrared energy. Windows employing low-e technology are known as spectrally-selective windows because of their ability to reduce solar heat gain without sacrificing light or visibility.

Window Placement and Shading

The most effective way to eliminate unwanted heat gain is to shade and place windows strategically and intelligently. Windows facing due north are the most ideal as they allow in a cool, even flood of light. The south windows also play a key role. The average home receives 10% of its heating needs quite by accident from ordinary south facing windows. However, during summer months, this unsolicited extra heat is quite undesirable and should be kept out by overhangs or some other exterior shading device. Windows facing east and west should be kept to a minimum and well shaded. In fact, all glazing, including north-facing glazing should have proper exterior shading. I cannot stress how important and effective it is to simply keep direct sunlight off of a building’s glazing. While interior shading devices, such as blinds, reflect some radiant heat, sunlight that has passed the glass barrier will contribute to heat gain. Remember, if it’s not shaded, you will pay for it (in your monthly electric bills)!

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